Satellite tracking explained

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The tags we use are known as Platform Transmitter Terminals, or PTTs for short. They are powered by an internal battery that is charged by a solar panel and sit comfortably on the back of the birds using a soft, light and strong harness made of Teflon.

While the tag is being fitted a dark hood is usually placed over the bird’s head to keep it calm. This is remarkably effective. The birds are very docile when handled this way and this minimises any stress and enables the whole fitting process to be completed in a matter of just a few minutes. The piece of white paper you can see in the picture is an insulator which is removed prior to the bird’s release, activating the device’s battery.

The birds we tag are typically incubating adults that are caught on the nest. Soon after tagging and release they go back to their nests, to resume incubation. Our studies over several years now show that fitting the tags actually disturbs the birds very little and they soon go about their normal lives, successfully rearing chicks and resuming their normal behavioral patterns as before.

The PTTs we are now using are the very latest technology available and quite literally state-of-the-art.  These new tags are only half the size of the originals, weighing just 5g and also transmit more frequently than the earlier device. The new tags are now so small and light they can be fitted to even the smallest Sociable Lapwings (generally the females) with no adverse side effects.

Every three days or so, the PTT starts to transmit a signal for a period of around 10 hours. Thousands of metres above, a fleet of satellites circle the Earth in polar orbit, meaning that as the Earth spins below them, they gradually pass over all points on the planet’s surface. If one of these satellites is passing over the tag while it is transmitting, it records the frequency and wavelength of the transmission, and uses the Doppler effect to estimate the position of the tag, often to within just a few kilometres. This information is then relayed to our conservation project scientists, allowing them to plot the bird’s movement and position. They then quickly pass the coordinates on to our project partners in the country in which the bird is passing through, so they can go into the field armed with the location of the migrating flock and track and monitor the birds. This also provides them the opportunity to take swift action if they find the birds are being hunted or persecuted in any way.